Interconnection element for multifiber cables

ABSTRACT

Multifiber interconnection element for optic fiber cable including two cylindrical complementary elements with optic fibers belonging to multifiber cables to be connected, abutted to the same. Each one of the complementary elements shows outside a longitudinal notch at least, having shape and size similar to the shape and size of a corresponding longitudinal slide obtained on the internal surface of a coupling bush. These complementary elements are inserted for reciprocal coupling inside this bush with the relevant front contact parts turned one against the other.

FIELD OF THE INVENTION

The present invention generally relates to optic fiber signaltransmission equipment.

More in particular, this invention concerns a multifiber connectordevice for optic fiber cables.

Different types of connectors are known and used for the realization ofconnections among optic fiber cables.

BACKGROUND ART

A first example of a typical multifiber connector, indicated as a wholewith 10, is shown in FIG. 1.

Connector 10 includes two coupling parts indicated with 13 and 13',respectively.

Inside part 13 of connector 10, a plurality of optic fibers 12 is housedand comes out from the end of an optic fiber tape 11.

Similarly, inside part 13' of connector 10, a plurality-of optic fibersis housed and comes out from the end of an optic fiber tape 11'.

On the front surface 15 of part 13 of connector 10, two guide holes 14are obtained.

Holes 14 are placed aside fibers 12 with longitudinal axis parallel tothe axis of the fibers themselves.

The front surface 15 of part 13' shows two pins 16.

Pins 16 are arranged aside the optic fibers 12' with longitudinal axisparallel to the axis of the fibers 12' and in a position coinciding toholes 14.

Connector 10 includes a clamping spring 17 to fix the two parts 13 and13'.

Through insertion of the two pins 16 inside the guide holes 14 opticfibers 12 alignment with optic fibers 12' is obtained and, consequently,the optic connection of cable 11 and cable 11 '.

Due to the action of the clamp 17, the two front surfaces 15 and 15' ofthe two parts 13 and 13' reciprocally adhere.

A serious problem associated to similar connectors is due to the factthat they do not allow satisfactory alignment of optic fibers abutted onthe two parts 13 and 13' of Connector 10.

In connector 10 of FIG. 1 the correct alignment of fiber is simplydetermined by the coupling between pins 16 and holes 14.

This mechanical coupling is absolutely insufficient to align opticfibers with the required very high accuracy.

To this purpose, it must be considered that the active core thickness ofan ordinary optic fiber is of 8 micron only.

Being the transmission coefficient between two coupled fibersproportional to the area of the contact front surface of fibersthemselves (hence, inversely proportional to the square of distancebetween axis of fibers) we can easily understand how a minimummisalignment among fibers (in the range of micron fractions) can lead tounacceptable attenuation of the signal.

To try to minimize this serious disadvantage, pins 16 and holes 14 aremade according to very high accuracy construction techniques, involvingan increase of realization costs and difficult construction processes.

Also, to allow the insertion of pins 16 inside guide holes 14, theexternal diameter of pins 16 must be slightly lower than the internalsection of guide holes 14.

The backlash associated to this small size difference is oftensufficient to impair the good quality of the optic connection offered byconnector 10.

The clamping action of the spring 17, required for the correct union ofthe two front surfaces 15 and 15' can distort the two parts 13 and 13'of connector 10, modifying the possible correct alignment of opticfibers.

To try to minimize these disadvantages, alternative solutions have beenproposed where said holes 14 are replaced by slides made on theconnector sides.

However, also in this case, the associated backlash between pins andslides is such to impair the good quality of the optic connectionoffered by the connector.

In summary, the optic connection offered by connectors of this type ischaracterized by attenuation values always rather high (1 dB approx.)and by the poor repetition capability of the signal attenuation valueduring the different insertions.

U.S. Pat. No. 4,898,449 discloses a connector including two couplingelements in each of which end parts light conducting fibers are securedin such a manner that the centers of their end faces are situated on oneline.

The connector further comprises a connector housing for receiving thetwo coupling elements. Each coupling element has a cylindrical outersurface and an orientation element which is capable of cooperating withan orientation member of the connector housing.

Said fibers are secured by means of a fiber holder heaving substantiallythe shape of a rectangular parallelepiped which is inserted into aninternal cavity of the relevant coupling element.

According to such a device, a good coupling between each pair of lightconducting fibers is performed if the fiber holder and the internalcavity are made with high precision.

OBJECT OF THE INVENTION

Object of this invention is therefore to supply a multifiber connectordevice for optic fiber cables allowing to obtain a good alignment ofoptic fibers to be connected.

An additional object of this invention is to supply a connecting devicesimple and stout, not showing the disadvantages of the above mentionedknown technique.

Particular object of this invention is to supply a reliable connectingdevice, not requiring for its implementation, the use of expensiveconstruction techniques.

DISCLOSURE OF THE INVENTION

These and other targets are reached through the invention consisting inan interconnection element for multifiber optic cables of the typeincluding:

a first and a second cylindrical ferrule, each having a longitudinalinternal cavity where said fibers to be interconnected are abutted, aportion of the external face of each cylindrical ferrule forming a firstflat surface;

a sleeve consisting of a cylindrical body, hollow inside, able toreceive said complementary cylindrical portions, the internal face ofwhich including a second flat surface;

orientation alignment means suitable to orient said fibers to beinterconnected; characterised in that said first and second cylindricalferrule have an opening so as to expose part of said internal cavity,and include:

fibers vertical alignment means in form of a third flat surface in atleast part which corresponds to said opening

fibers lateral alignment means, in form of a fixing plate heavinglongitudinal "V" shaped grooves, for the housing and lateral positioningon said third flat surface of said multifiber optical cable.

According to the invention, with a very simple construction, a ferrulecan be made in which only the first flat surface and the flat surface ofthe internal cavity. i.e. the third flat surface have to be made withprecision.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The invention,together with further objects and advantages thereof, may be understoodwith reference to the following description, taken in conjunction withthe accompanying drawings, and the several figures of which likereferenced numerals identify like elements, and in which:

FIG. 1, already described, shows a perspective view, in partial sectionof a known multifiber connector;

FIG. 2, shows a perspective view of two ferrule and one alignment bushof a multifiber connector according to the present invention;

FIG. 3 shows the section of the two ferrule of FIG. 2 coupled throughthe above mentioned bush;

FIG. 4 shows the section of the connector made according to plan IV--IVof FIG. 2;

FIG. 5 shows the connector section made according to plan V--V of FIG.2;

FIG. 6 shows the silicon plate 38 of FIG. 3 used for the positioning offibers inside the connector;

FIG. 7 shows a section of one of the two ferrules of FIG. 1 madeaccording to plan VII--VII of FIG. 4;

FIG. 8 shows a second embodiment of bush 23 of FIG. 2;

FIG. 9 shows the structures, plastic material made, destined to housethe bush 23 and the two ferrules 21 and 22 of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Making reference to FIG. 2, two ferrules belonging to the twocomplementary elements of a connecting device according to the presentinvention are indicated 21 and 22, respectively.

An alignment bush for the two ferrules 21 and 22 was indicated with 23.

The ferrule 21 is ceramic material made, such as for instance alumina orzirconia and has cylindrical shape.

Referring to FIGS. 2 to 6 the structure of ferrule 21 will be shown. Thecomplementary ferrule 22 shall not be described, being complementary toferrule 21 as it can be clearly noticed from FIG. 3.

Ferrule 21 shows inside a longitudinal slide, crossing it from one endto the other one.

The longitudinal notch has rectangular shape with rounded edges andinside the same a 24 optic fiber tape is inserted.

In the particular embodiment shown, the tape 24 consists of four opticfibers.

Generally, this tape 24 can consist of a different number of fibers.

Close to the end to be coupled, the ferrule 21 shows on its side surfacea flaring 25 having flat rectangular shape.

Usefully, flaring 25 is obtained through grinding of the lateral surfaceof ferrule 21.

Flaring 25 identifies an opening 36 (see FIG. 3) enabling access to saidlongitudinal notch starting from the lateral surface of ferrule 21.

Coinciding the opening 36, the longitudinal notch shows, on the sideopposite to opening 36 itself, a 37 rectangular step, having sizeessentially similar to the size of opening 36.

The height of step 37 is equal to one half the height of notch 36,decreased by half thickness of a fiber without external protection(typically 25 micron).

Matching step 37, optic fibers of tape 24 are cleared from the externalprotection. Their diameter assumes then 125 micron value.

Fibers of tape 24, made free from the external protection, rest on step37. Due to the thickness of step 37, fibers assume a position such thatthe longitudinal axis of each fiber lays on the mean longitudinal planof the longitudinal notch.

A plate 38 for fiber fixing (see also FIG. 6) in placed above step 37.On one side of plate 38, four `V` shaped grooves 61 are obtainedsuitable to receive said fibers.

This step creates in fact a flat surface, resulting parallel to the plansurface consisting of said notch 28.

In particular, considering that on said step, fibers rest and theiralignment in respect with the fibers of the complementary connectormainly depends on the accuracy employed to determine their distanceversus the reference plan consisting of said notch 28, the step isrealized with tolerance lower than μm.

FIG. 6 shows in detail the arrangement of the four grooves 61, withoutfibers housed.

Preferably the plate 38 is made of silicon.

Plate 38 is rested on the step 37 with the grooved 61 side downward.

The silicon plate 38 is joined to the step 37 with bonding agents orresins.

The above mentioned longitudinal notch is partly filled with fixingmaterial 39, one optic fibers of the tape 24 and plate 38 are inserted.

The fixing material 39 is preferably argentana. This material ischaracterized by a lower hardness compared to the material of opticfibers.

Particularly referring to FIGS. 2 and 3 the end 26 of ferrule 21 shows acontact front part 27, consisting of the front edge of ferrule 21itself, of the longitudinal notch filled with the fixing material 39 andof contact sides of optic fibers.

In the embodiment shown in FIG. 3 this end 27 has flat shape and shows aslight slope (8° approximately) from top to bottom.

In the embodiment shown in FIG. 7 this end 27 has rounded shape.

The shape of end 27 is made in the working phase of ferrule 21 through alapping and polishing operation involving the ferrule edge, the fixingmaterial and fibers at the same time and consequently the front side ofthe ferrule shall result rounded both in respect with the horizontalaxis and versus the vertical one.

Referring to FIGS. 2 and 8 the structure of the alignment bush 23 willbe shown.

Bush 23 is phosphorous made of bronze or zirconia and has cylindricalshape, according to a preferred embodiment.

The internal surface of bush 23 shows a longitudinal reference guide 81preferably crossing the bush 23 along the whole length.

The longitudinal guide 81 has rectangular flat shape and has widthcorresponding to the notch 28 width, preferably consisting of said flatsurface of ferrule 21.

On the internal surface of the bush 23, at the edges of guide 81, twolongitudinal channels 82 and 83 are obtained, having the function toneatly separate the circular surface of said fiat surface of notch 81.

Bush 23 shows a slot 84 giving elasticity to the bush itself.

In the embodiment shown in FIG. 2 the slot 84 is longitudinal while inthe embodiment shown in FIG. 8 it is an helical slot.

The two complementary ferrules 21 and 22 are inserted one in front ofthe other in the two opposite openings of bush 23 in order that thelongitudinal guide 81 of bush 23 slides in notch 28 of each one offerrules 21 and 22.

It is evident that resting the flat surface 28 on the flat surface 81,fibers shall result perfectly aligned is the above mentioned step 37 ismade with due accuracy,

Referring to FIG. 9 covering and support elements for ferrules 21 and 22and for bush 23 shall be described.

Covering and support elements described hereafter are essentially of theknown type.

The cylindrical bush 23 is placed inside two sleeves 91 and 92.

These sleeves are fit with a longitudinal hole 93 destined to house thebush 23 and, after insertion of the same, sleeves 91 and 93 are joinedtogether, for instance through gluing.

Ferrules 21 and 22 are on the contrary partially inserted in a samenumber of handles 94 and 95 from which fiber tapes 24 come out.

The advantages of the invention are evident.

Due to the "V" grooves fibers are arranged with high accuracy on plate38. The Plate 38 is fixed in its turn with high accuracy, to a flatsurface parallel to said notch 28, inside the longitudinal notch offerrules 21 and 22.

The longitudinal guide 81 of bush 23 assures, engaging against notch 28of ferrules 21 and 22, a correct alignment of the same and consequently,a correct alignment of optic fibers belonging to tapes 24.

Alignment between ferrules 21 and 22 assured by flat surfaces foreseenon ferrules 21 and 22 and on bush 23 results to be more accuratecompared to the alignment given by any other coupling system based onpins or guides. In fact, from an implementation point of view, itresults easier to realize the flat surface of notch 28 and of guide 81of the bush, than an alignment system realized with cylindrical elementssuch as pins and guides.

Typical attenuation values offered by connectors according to thepresent invention are of 0.3 dB approximately, much better than typicalattenuation values offered by said known connectors.

The optical connection offered by the connector according to theinvention is characterized by the good repetition capability of thesignal attenuation value during the different insertions.

Where required, it is possible to furtherly increase the accuracy of theconnector, increasing the number of notches 28 present on ferrules 21and 22 and, similarly, obtaining an equal number of longitudinal guides81 on the internal surface of bush 23.

In this case, the embodiment of the bush shown in FIG. 8 resultsadvantageous compared to the embodiment of the bush in FIG. 2, since itmakes easier the realization of a second guide element 81. Also, thisembodiment of bush 23 imposes an evenly distributed stress on the wholelateral surface of ferrules 21 and 22, contributing to diminish the riskof breaks and distortions.

The fact that the fixing material 39 (argentana) for fibers is softerthat the material of optic fibers, offers number of advantages.

When the ends 27 of the two ferrules 21 and 22 come in contact, thefixing material 39 distorts until the fibers of the two ferrules 21 and22 touch each other,

In FIG. 3 the front side of the two ferrules, has been shown for graphicrequirements before these units are submitted to lapping. However, it isevident for a technician of the field that after this operation is madefibers shall result directly in contact or the fixing material first,then fibers, due to the distortion of this material.

This distortion determines an "fitting effect" of the ends eliminatingthe presence of air gaps due to errors in the lapping process.

It must be highly appreciated the fact that both ferrules 21 and 22 andthe bush 23 have cylindrical shape, which enables to employ the samecovering elements (91, 92, 94, 95) and support elements used for singlefiber connectors, without the need-of any modification.

While a particular embodiment of the present invention has been shownand described, it should be understood that the present invention is notlimited thereto since other embodiments may be made by those skilled inthe art without departing from the scope thereof. It is thuscontemplated that the present invention encompasses any and all suchembodiments covered by the following claims.

We claim:
 1. Interconnection element for multifiber optic cablescomprising:a first and a second cylindrical ferrule, each having alongitudinal internal cavity in which said fibers to be interconnectedare abutted, a portion of the external face of each cylindrical ferruleforming a first flat surface; a sleeve consisting of a cylindrical body,hollow inside, able to receive said complementary cylindrical portions,the internal face of which has a second flat surface; and orientationalignment means suitable to orient said fibers to be interconnected;wherein said first and second cylindrical ferrules have an opening so asto expose part of said internal cavity, and include; fibers verticalalignment means in the form of a third flat surface in at least a partwhich corresponds to said opening, and fibers lateral alignment means,in the form of a fixing plate having longitudinal "V" shaped grooves,for the housing and lateral positioning on said third flat surface ofsaid multifiber optical cable.
 2. The element according to claim 1,wherein said fixing plate is made of semiconductor material.
 3. Theelement according to claim 1, wherein said third flat surface isparallel to said first flat surface.
 4. The element according to claim1, wherein each one of said hollow cylindrical portions are filled,coinciding to the front contact part of said optic fibers with fixingmaterial softer than the material optic fibers are made.
 5. The elementaccording to claim 1, wherein the lateral surface of said sleeve has alongitudinal slot.
 6. The element according to claim 5, wherein saidlongitudinal slot is a straight shaped slot.
 7. The element according toclaim 5, wherein said longitudinal slot is a helical shaped slot.
 8. Theelement according to claim 1, wherein said sleeve is made of phosphorousbronze.
 9. The element according to claim 1, wherein said sleeve is madeof zirconia.
 10. The element according to claim 4, wherein said fixingmaterial is argentana.
 11. The element according to claim 1, whereinfront contact parts of said complementary cylindrical portions aresmaller than cross sizes of said complementary portions.
 12. The elementaccording to claim 1, wherein said front contact parts of saidcomplementary cylindrical portions are flat and slightly sloped.
 13. Theelement according to claim 12, wherein said slight slope is 8° slope.14. The element according to claim 1, wherein front contact parts ofsaid complementary cylindrical portions are rounded.
 15. The elementaccording to claim 1, wherein said opening and said third flat surfacein said first and second cylindrical ferrules are obtained by grindingthe lateral surface of the same complementary cylindrical ferrules.